This invention relates in general to auxiliary contacts for suppressing arcing in a switch, and more particularly to arcing contacts for a blade knife switch having a high current carrying capacity.
In many high current applications, it is necessary to provide a switch in the circuit to rapidly supply or interrupt the current. The currents are typically in the range of 5,000 to 55,000 amperes per blade and termination and 150,000 amperes per switch. One illustrative application is in the electrolytic production of chlorine gas. The chlorine is generated in electrolytic cells which operate continuously with currents in excess of 50,000 amperes. However, when a cell needs to be refurbished, or if there is a failure in a critical operating component, such as a mercury pump which prevents an explosive accumulation of hydrogen, it is necessary to apply a shorting switch across the terminals of the cell.
Interruption of very high currents can produce voltage surges even with very low inductance present such as the self inductance of straight flat copper bus bars. Such voltage surges may be in excess of those which ionize air and may add substantial energy dissipation requirements to the arcing contacts. Arcing between the switch members promoted by the ionized air is extremely troublesome since it erodes or pits the contact surfaces of the switch members which increases the switch resistance and eventually renders it useless, or in extreme cases, welds the switch members together. A related problem, commonly termed "spitting", occurs when the initial or final contact points of the switch members become rapidly heated to such a high degree that they liquify and spit off some of their component material.
A well known solution is to provide a low resistance shunt between the switch members in the form of an arcing contact. More specifically, laminated arcing contacts have been used in circuit breakers and transfer switches. However, no arcing contact heretofore known is capable of repeated, reliable operation at the high current levels described above. Conventional arcing contacts either fail to have a sufficiently large cross-sectional area (and hence very low resistance) to accommodate high currents, or fail to establish a good contact across the switch members. In addition, conventional arcing contacts will frequently gouge or score the switch termination as the switch blade moves into or out of the fully closed position, or, the arcing contact will bounce out of contact with the termination during a rapid cycled opening and closing of the switch. Another difficulty is that many conventional arcing contacts are not adaptable to a bolted contact knife switch which is a type frequently used in high current applications.
It is therefore a principal object of the invention to provide an arcing contact for a high current switch that eliminates arcing between its relatively movable switch members which arcing may result in the erosion, pitting, spitting or welding together of the members.
Another object of this invention is to provide an extremely low resistance arcing contact which maintains a good electrical connection between the switch members as the switch makes or breaks.
Still another object of the invention is to provide an arcing contact which does not score or otherwise damage the switch members, or bounce during rapid cycled operation.
Still another object of the invention is to provide an arcing contact for a high current switch which is conveniently replaceable and adjustable and has a low cost of manufacture.
Yet another object of the invention is to provide an arcing contact as described above which is reliable and has a long operational life.